Recently, researchers have tried to exploit the natural ability of RNAs to mobilize and transcript genetic information for therapeutic purposes. Such methods normally involve the interference with dysfunctional nucleic acids or proteins and/or the stimulation of the production of therapeutic genes. Particularly important is a process that uses synthetic double-stranded RNA, known as RNA interference (RNAi). This operates via post-transcriptional gene silencing, mediating the resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and therefore regulating the expression of protein-coding genes. It appears evident that the efficient cytosolic delivery of RNAs is a vital step in almost all RNAi-based gene-silencing experiments. Efficient cytosolic delivery of nucleic acids is, however, a very difficult task. Synthetic siRNAs can be delivered to cells in culture via electroporation or by using either cationic lipids or polymers. However, these approaches are limited by the transient nature of the response and in some cases by vector-mediated toxicity, (Mittal, V. Improving the Efficiency of RNA Interference in Mammals. Nature Rev. Genet. 5, 355-365 (2004)).
WO2002/044321 describes the sequence and structural requirements for small RNAs mediating RNA interference and therapeutic uses of interfering RNA. Using a drosophila in vitro system, it is demonstrated that 19-23 nucleotide short RNA fragments are the sequence-specific mediators of RNA.
Alnylam Pharmaceuticals Inc. have developed a variety of therapeutic compositions comprising siRNAs. Some of these are disclosed in, for instance, WO2004/030634. Sirna Therapeutics, Inc. are also active in this area. Their U.S. Pat. No. 7,022,828, for example, describes siRNA treatment of diseases or conditions related to levels of IKK-gamma.
EP1527176 describes novel forms of interfering RNA molecules. The molecules are double-stranded structures in which the strands are at least partially complementary to one another, and wherein the double-stranded structure is blunt ended. WO02006/069782, by the same Applicant, describes delivery agents for introducing small nucleic acids, such as those in EP1527176, into cells. The delivery agents are lipid compositions comprising a first lipid component, a first helper lipid and a shielding compound (for instance PEG) which is removable from the lipid composition under in vivo conditions.
We have recently reported on a very efficient, non-toxic and non-inflammatory vector for the delivery of (plasmid) DNA within human cells, (Lomas, H. et al. Biomimetic pH Sensitive Polymersomes for Efficient DNA Encapsulation and Delivery. Adv. Mater. Vol 19 (2007), 4238-4243). The combination of this type of polymer with DNA is described in our patent application WO03/074090. In this application, 2-(dimethyl) ethyl methacrylate (DMA)—MPC polymers are used to form DNA-polymer complexes. Depending upon the block lengths and pendant groups of the respective components of the copolymer, it is now known that the interaction with DNA can be tailored to produce DNA condensates (polyplexes) or have the DNA encapsulated within a vesicle of the material. The latter is based on the self-assembly of pH sensitive poly (2-methacryloxyethyl phosphorylcholine)-poly (2-(diisopropylamino)-ethyl methacrylate), (PMPC-PDPA) block copolymers into nanometer-sized vesicles, also known as polymersomes, (Du, J., Tang, Y., Lewis, A. L. & Armes, S. P. pH-Sensitive Vesicles Based on a Biocompatible Zwitterionic Diblock Copolymer. J. Am. Chem. Soc. 127, 17982-17983 (2005)).
Tan et al in Biomacromolecules 2007, 8, 448-454 describe polyethylene oxide-poly(dimethylamino)ethyl methacrylate (PEO-b-PDMA) and PEO-b-poly(diethylamino)ethyl methacrylate (PEO-b-PDEA) copolymers as a self-assembling non-viral vector for plasmid DNA delivery. Similarly, Tan et al in Langmuir vol, 22 No. 8, 2006, 3744-3750 describe complexes of PEO-b-PDEA copolymers with plasma DNA. Neither of these references discuss the formation of complexes with smaller strands of nucleic acid.